Vapour phase ammoxidation has become an important technology. The vapour phase ammoxidation technique is a highly advantageous and a very simple method of producing nitriles in a single step and bears many superior qualities like high purity of the product, higher yields, low cost, continuous process and almost no environmental pollution. The vapour phase ammoxidation technique involves the usage of ammonia and air to convert an active methyl moiety into a cyano moiety in one step using a catalyst. This type of technique can for instance be used to prepare benzonitriles, the compounds that are derived from benzene derivates in which a methyl moiety is converted into a cyano moiety.
Halogenated benzonitriles consists of benzonitriles, which bear one or more halogen atoms, such as fluorine, chlorine, bromine or iodine. A particular example is 2,6-dichlorobenzonitrile (2,6-DCBN). In the recent years, there has been an increasing demand for 2,6-dichlorobenzonitrile (2,6-DCBN) due to its wide use in the chemical industry. It is an effective weed killer per se. Once 2,6-DCBN is used as weedicide, it is expected to be effective for a long period of time and prevents the growth of weeds even for many years. In addition, the toxic effects of 2,6-DCBN towards mammals are reported to be very low. 2,6-DCBN is also an important intermediate for agricultural chemicals and medicines. Many agricultural chemicals such as flufenoxuron, flucycloxuron, hexaflumuron, chlorfluazurin, diflubenzuron, teflubenzuron etc. can be prepared from 2,6-DCBN. 2,6-DCBN is also a starting material for preparing insecticides. In addition, 2,6-DCBN is also used to prepare polyphenyl ether hydrocyanic ester, which is one of the best kinds of special engineering plastics with the most outstanding features in today's world.
The preparation of halogenated benzonitriles in general is a very challenging task. Because of the presence of halogen atoms, the accessibility to the methyl moiety for N-insertion is restricted as a result of steric hindrance. In particular, the preparation of 2,6-dichlorobenzonitrile (2,6-DCBN) from 2,6 dichlorotoluene (DCT) is difficult as a result of the steric hindrance caused by the presence of the two bulky chlorine atoms on both the ortho positions of the methyl moiety in 2,6-DCT.
Methods to prepare 2,6-DCBN through vapour phase ammoxidation of 2,6-DCT over catalysts are known from the European patent application No. 0 273 317, which discloses the use of a multi-component catalytic system comprising Fe—Sb—V—Cr—O/SiO2 for the ammoxidation of 2,6-DCT, and from U.S. Pat. No. 4,530,797, which describes a method for the ammoxidation of 2,6-DCT using VPO/SiO2 as a catalyst, both carried out using fluidised bed reactors. This type of reactors shows disadvantages including a great demand on mechanical stability of a catalyst against abrasion. In addition, these documents do not describe methods whereby a high conversion of more than 99% of 2,6-DCT can be obtained. This implies that these methods still show additional separation or recycling costs. Furthermore, the described methods show many disadvantages from industrial production point of view such as low space-time yields, very high residence times and low inputs of 2,6-DCT per unit weight of the catalyst used.
Therefore, it is an object of the present invention to provide an improved vapour phase ammoxidation method, which overcomes the above-mentioned disadvantages. More in particular, the present invention provides an Improved method for obtaining 2,6-DCBN by vapour phase ammoxidation of 2,6 DCT, by a process carried out In a fixed bed reactor. Compared with known methods of 2,6-DCBN preparation by vapour phase ammoxidation, the present invention provides an improvement of several reaction parameters. Another object of the invention consists of providing higher molar yields. Yet another object of the invention is to obtain higher space-time yields. Also, the invention aims to provide higher conversion rates of 2,6-DCT.
Further, it is also an object of the Invention to provide a suitable catalyst for carrying out the vapour phase ammoxidation method. The invention also aims to provide an easy method for preparing the catalyst for use In the vapour phase ammoxidation process.